(a) Technical Field
The present disclosure relates, generally, to a humidifier for a fuel cell. More particularly, it relates to a humidifier for a fuel cell, in which a plurality of hollow fiber membranes having different diameters are appropriately arranged to control the flow direction of dry air introduced into the humidifier, thus suitably uniformly humidifying the dry air.
(b) Background Art
An electrolyte membrane in a fuel cell is preferably humidified for the operation of the fuel cell, and, accordingly, a humidifier which performs humidification by water exchange between exhaust gas (humid air) discharged from the fuel cell and dry air supplied form the outside is used.
In particular, a compact humidifier which consumes less power and requires a small installation space is required in a fuel cell. Although there are various types of humidifiers such as an ultrasonic humidifier, a steam humidifier, an evaporative humidifier, etc, a humidifier using hollow fiber membranes is suitably used in the fuel cell.
As shown in FIG. 1, a typical air supply system in a fuel cell system includes a membrane humidifier 100, in which dry air is supplied from the outside by an air blower 202 and, exhaust gas discharged from a fuel cell stack 200 passes through the membrane humidifier 100 such that the dry air is humidified by water contained in the exhaust gas while passing through hollow fiber membranes provided in the membrane humidifier 100.
FIG. 2 is a cross-sectional view showing the configuration of an exemplary hollow fiber membrane humidifier.
As shown in FIG. 2, the humidifier 100 preferably includes a housing 101. The housing 101 preferably includes a first inlet 102 through which dry air is suitably introduced and a first outlet 103 through which humidified air is suitably discharged. In particular, a hollow fiber membrane module 107 is suitably disposed in the inside of the housing 101, and a plurality of hollow fiber membranes 106 are accommodated in the hollow fiber membrane module 107.
In the humidifier 100 using the hollow fiber membranes 106 with the above-described configuration, when exhaust gas (humid air) discharged from the fuel cell stack is supplied to the inside of the housing 101 through a second inlet 104, the water in the exhaust gas is separated by capillary action of the hollow fiber membranes 106, and the separated water is condensed while passing through capillary tubes of the hollow fiber membranes 106 and collected in the hollow fiber membranes 106.
Then, the exhaust gas, from which water is separated, moves to the outside of the hollow fiber membranes 106 and is discharged to the outside through a second outlet 105 of the housing 101.
Further, outside air (dry air) is supplied through the first inlet 102 of the housing 101 by the operation of the air blower and passes through the hollow fiber membranes 106. Accordingly, since the water separated from the humid air is collected in the hollow fiber membranes 106, the dry air is suitably humidified by the water and then supplied to the fuel cell stack through the first outlet 103.
As shown in FIG. 2, since the plurality of hollow fiber membranes 106 are suitably concentrated in the hollow fiber membrane module 107, it is difficult for the humid air introduced through the second inlet 104 to permeate through the hollow fiber membrane module 107. In particular, the rate at which the humid air is diffused into the hollow fiber membrane module 107 is very low, which makes it more difficult for the humid air to permeate through the hollow fiber membrane module 107.
Accordingly, the humid air passing through the outside of the hollow fiber membrane module 107 accommodated in the housing 101 does not penetrate into the center of the hollow fiber membrane module 107 as shown in the dotted line box of FIG. 2 but mainly flows along the periphery of the hollow fiber membrane module 107 as shown by the arrows of FIG. 2. As a result, the rate at which the humid air is diffused into the hollow fiber membrane module 107 is suitably reduced, which decreases the humidification efficiency.
Accordingly, the hollow fiber membranes 106 located in the center of the hollow fiber membrane module 107 cannot be suitably supplied with sufficient water, and thereby the overall efficiency of the membrane humidifier is reduced.
Further, in the conventional membrane humidifier, the dry air introduced through the first inlet 102 mainly flows through the center (as shown in the dotted line box of FIG. 2) of the hollow fiber membrane module 107, and as a result the efficiency of the membrane humidifier is further reduced.
This is illustrated in the simulation test results of FIG. 3.
It can be clearly seen from FIG. 3 that most of the dry air flows only through the center of the hollow fiber membrane module 107.
Accordingly, since the dry air introduced through the first inlet 102 mainly flows through the center of the hollow fiber membrane module 107 (as shown in the dotted line box of FIG. 2) and the humid air introduced through the second inlet 104 flows along the periphery of the hollow fiber membrane module 107, the overall humidification efficiency of the humidifier may be suitably reduced.
Such a problem becomes more serious when the amount of dry air is large, i.e., when the fuel cell stack provides high power output.
Another problem of the conventional humidifier is caused by the hollow fiber membranes and the arrangement thereof.
Despite the advantage that the membrane humidifier is applicable for use with a vehicle, available hollow fiber membrane materials are very expensive, and thus it is the manufacturing cost is high.
In most cases, sufficient humidification is required in a low current region of the fuel cell system, and much water is produced in high power and high current regions to the extent that a cathode does not require humidification. Nevertheless, most of the conventional humidifiers are operated without varying the amount of humidification in both the low and high current regions. In particular, in the case where the hollow fiber membranes are made of only Nafion, a high humidity of more than 80% RH is provided even in the high current region.
Further, a bundle of hollow fiber membranes having the same diameter is disposed in the conventional membrane humidifier, and the hollow fiber membranes are made of expensive Nafion, which is disadvantageous in terms of manufacturing cost.
Since a large amount of water is produced and a high humidity is provided in the high current region of the fuel cell system, an increase in resistance of cathode material transfer and a flooding phenomenon may occur, which results in air starvation of the cathode. As a result, the deterioration of the fuel cell catalyst is accelerated and thus the durability of the fuel cell is suitably reduced.
Accordingly, there is a need in the art for humidifiers for a fuel cell.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.